While LED lighting elements with their inherent advantages such as high efficiency and long lifetime are already used in many applications today, the use in automotive front lighting is still limited.
Already today, LED lighting elements are available with sufficient luminous flux for automotive front lighting. For example, LUXEON Altilon LED elements available from Philips Lumileds are designed for such applications.
However, LED elements are generally Lambertian emitters, i.e. do not generate a directed beam of light. On the other hand, motor vehicle headlamps are required to emit a specific beam pattern. For a low beam light, the beam pattern must have a sharp light/dark cutoff, i.e. a horizontal or slightly inclined line, below which the road ahead of the vehicle is brightly illuminated, whereas above the bright/dark cutoff line light is shielded to avoid glare.
WO 2006/033042 describes a lighting arrangement with an LED lighting element, where a desired beam is formed by a collimator element and by secondary optics. The collimator comprises opposing first and second reflector faces arranged close to the LED element. The first reflector face has a first edge, where a sharp cutoff is produced. The second reflector face has an upper section arranged inclined to a sectional plane and a lower section with less inclination. The LED collimator element is further delimited by lateral reflector faces, which are inclined outwards in the emission direction.
DE 10 2009 037 698 describes an automotive lighting unit. Light emitted from an LED light source is formed into a light pattern by an optical element, and a lens is used to project the light pattern. The optical element comprises a first reflective surface arranged horizontally under the optical axis of the LED light source and a second reflective surface above the optical axis. The first reflective surface comprises an edge of elliptical shape, which is arranged within a focus group of the projection lens. The second reflective surface is bent conically and is shaped to have a focus at or near the LED light source. A resulting light pattern comprises a portion of light Ha emitted directly from the LED element without reflection, a portion Hb reflected at the first reflective surface, and a portion Hc reflected at the second reflective surface.
US 2009/0122657 discloses a projection-type light source unit with an LED module as light emitting device, a reflector, a cut-off line forming shade, and a projection lens. The optical axis of the LED chip is oriented in a direction perpendicular to the optical axis of the light source unit. Light emitted from the LED chip is reflected by a reflector and concentrated at a point A near the rear focus of the projection lens. The projection lens projects an image formed on the focal plane, so that a light distribution for low beam with a clear cut-off line is formed.
WO 2009/122364 describes a projection module for a motor vehicle headlamp. An LED light source is surrounded by a reflector housing used as a collimator. A horizontal lower edge of the collimator lies on the centre axis of a lens, and is positioned within the focal plane of the lens, having a curvature corresponding to the different geometric spacings of the edge. The edge is provided with a 15° slope to generate a desired light distribution with a light-dark boundary for a low beam headlamp.